1. Field of the Invention
This invention relates to a computer-aided product design system, more specifically, a product design system constituted as the so-called CAD (computer-aided design)/CAM (computer-aided manufacturing), CIM (computer-integrated manufacturing) and other product design systems.
2. Description of the Related Art
The technology taught by Japanese Laid-Open Patent Application Hei 9-319,772 can be given as an example of this kind of computer-aided product design system. In this prior-art, the features of the product shape are determined in the preceding product design process, thus facilitating automated design of the upper mold shape in the mold design process in the subsequent process, whereby shortening of the period of time to design in both processes is possible.
In CAD/CAM or CIM, when molds are used to manufacture products, the designer normally uses a CAD system to first make or design a product model or product shape and the product model is then used to make or design a mold model in the mold design process. Next, this mold model is used to make mold fabrication data, after which the mold is fabricated by CNC (computer numerical control) fabrication, etc., using the data, and the fabricated mold is used to make the product by casting or cutting.
In this way, the shape of the product model constructed in the product design process determines the shape of the product, and therefore the release draft, i.e., the release draft for releasing the product from the mold required for the casting process, must be added to the product model in the product design process.
A rounded portion referred to as a fillet is applied or formed on a square edge in this product model. Specifically, the product model is edited such that portions where two lines or curves intersect continue smoothly with a circular arc (fillet) having designated or specified radius of curvature.
In the prior art product design process using CAD/CAM or CIM, first the release draft is formed in the product model, and the fillet is applied or formed. This is because in the prior art product design process, the shape of the model is described, by using an edge often referred to as a winged edge, and by defining the relationship of the edge containing its left and right surfaces and points. If a fillet is applied, the edge disappears. For that reason, the fillet is formed at a relatively later stage. The fillet is added with the intent of improving appearance and in addition to avoiding the concentration of stress in the product (and mold).
However, it is desirable for the engineer (designer) that the fillet be applied in the initial stage of the product design process such that he can do the work while confirming or verifying the function of the product based on the product model or product shape with the fillet applied.
Further, when a product is given a complex shape with continuous uneven portions such as in the transmission case of a vehicle, a release draft must be formed or applied to each uneven portion and judgment must be made as to whether the formed release draft is sufficient to release the product from the mold, after which the operation of applying fillet must be performed. In this case, if the formed release draft is to be changed for some reason, the uneven portions must first be corrected, after which the release draft is corrected, resulting in a tedious operation.
Further, in order to form a release draft or fillet in a partial area of an uneven portion in the prior art product design process using CAD/CAM or CIM, since the entire of the uneven portion should necessarily be selected or designated automatically, the process of selecting a partial area of the uneven portion must be done by designating the mold parting plane, mold release direction, etc. Thus, the prior art product system is not satisfactory in the freedom of design and leaves much to be improved.